One prior art type of programmable attenuator includes a plurality of attenuator sections, each connected to terminals of a double pole, double throw relay to be switched into or out of a serial energy transmission path and to obtain an amount of attenuation which is controllable in steps by selective control of the relays. For example, with a series of four sections having attenuations of 1 dB, 2 dB, 4 dB and 8 dB, it is possible to obtain attenuation of from zero to 15 dB in 1 dB steps. One programmable attenuator of this type is illustrated in the Patukonis U.S. Pat. No. 4,330,765. Such attenuators may be used to obtain quite satisfactory results in many applications. However, they have had limitations with respect to the amount of attenuation which might be obtained in one section and with respect to the highest frequency at which a flat response can be obtained. Also, they have used relays of a special parallel DPDT (double pole, double throw) configuration such as to provide alternate parallel non-crossing paths between two sets of terminals, one path using a minimum or "zero" attenuator. The avoidance of crossing paths has advantages but such relays are expensive and this type of attenuator has otherwise been costly to manufacture.
There are other types of attenuators in the prior art, including push-button actuated, rotary or other mechanically actuated attenuators and solid state attenuators but all known types of attenuators have features such that they are not readily controlled from a remote location, or they have reliability problems, or the frequency range of operation is limited at either the high end or the low end or they are too large in size or too expensive to manufacture or have other disadvantages.